1. Technical Field of the Invention
This invention relates to devices for aiding in weight distribution and support of back borne loads, and more particularly to adding internal, load bearing support to the spine and shoulders through application of abdominal wall pressure, to the external load support provided by a hip belt and backpack load carrier.
2. Background Art
Man""s skeletal and muscle structure, upright carriage, and bipedal mode of locomotion, whether walking or running, requires a large degree of freedom of shoulder, back, arm and hip movement to facilitate a coordinated gait and maintain balance. This is particularly true for traveling a significant distance and for traversing other than a level surface. A healthy person is generally capable of lifting and transporting in his or her arms roughly up to about one half of his or her own weight for short distances.
It is common knowledge that the load bearing capacity of a person can be greatly enhanced by placing the load on their back, and more specifically, by the use of a backpack load carrier. A backpack can be minimally described as a container or load of any sort that is equipped with straps by which it can be attached to a person""s back. The straps may be attached to the load or pack by only one end, being then disposed over one or both shoulders and grasped and held at the user""s chest.
More commonly, in order to keep the hands and arms free for coordinated walking motion and other uses, the other end of the strap or straps are attached at a lower point on the load as a shoulder strap, so as to distribute the pack load between the two attach points. Where there are two straps, the upper and lower attach points are likely to be spaced apart, equal distance from the centerline of the load or pack. The length of the two straps are typically adjusted to about the same, depending on the user""s normal posture and carriage, so that the pack is more or less laterally centered on the back.
Backpacks are common gear for hikers, in particular. They are used to carry equipment and food for the hiker on trips extending from short day trips through a city park to rigorous overnight trips through remote wilderness areas where the right equipment can be vital to the hiker""s survival. The longer and more remote the route of the trek and the more rigorous the terrain, the more important it is for the backpack to be as comfortable as possible for the hiker.
A common, secondary source of support for the weight of a shoulder strap backpack is the additional use of a hip belt, to which the backpack is also attached. The hip belt, utilized in conjunction with the shoulder straps to shift part of the load directly to the hips or pelvic region, decreases the weight bearing directly on the shoulders and skeletal spine.
This mode of augmented support of the back borne load is commonly accomplished by suspending the backpack on the hiker""s back with two padded shoulder straps and using an adjustable hip belt which encircles the hiker""s pelvis and is joined in the front of the hiker""s abdomen with a belt buckle; the shoulder straps and hip belt being attached to the backpack. The hip belt serves to transfer a portion of the weight of the backpack to the pelvis of the hiker, while the shoulder straps both bear weight and secure the load to the hiker""s back. In so doing, much of the weight of the backpack is now supported by the pelvis of the hiker through the external attachment of the backpack to the hip belt, rather than by the hiker""s skeletal spine.
However, for the hip belt to transfer the weight effectively from the backpack to the pelvis, the hip belt must be worn snugly around the user, necessarily impinging on the hiker""s pelvis. For this reason, the strap or web portion of the hip belt covering the hips, is often made somewhat wider than a common trouser belt, typically two or three inches wide in order to distribute the weight bearing on the pelvic region. Adding some width to the hip belt alleviates the problem to some extent, but does not completely prevent the hip belt from impinging on the pelvis. Making the web or strap portion of the belt much wider than two or three inches restricts the hikers maneuverability and reduces the belt""s utility.
However, extra width in the web section of the belt does nothing to prevent a hard belt buckle on what is typically a narrower front section of the belt, from pressing into the abdomen. Buckle padding, where provided, is generally soft and flexible and only slightly oversize compared to the buckle. This relieves only the sharpness or hard edges of the buckle hardware. Loosening or opening the belt in an effort to decrease discomfort from either or both of the impinging buckle in the abdomen or the rubbing and riding web section of the belt on the hips, results in more or all of the load being carried by the shoulder straps, placing the load back onto the spine and defeating the benefit of the hip belt.
Pads are often added to the back and sides of the hip belt to further reduce the pressure around the pelvis. Some pads extend from the back of the hiker, around to the hiker""s Anterior/Superior Iliac Spines (ASIS) of the pelvis. The ASIS form the bony landmarks in the front of the pelvis on either side of the abdomen. If the pads extend much past the ASIS, the hip belt becomes difficult to adjust and may not be able to be properly tightened around the hiker""s pelvis.
Beyond the mere discomfort and superficial sore spots associated with inadequate designs and ill-fitted or improperly rigged packs with hip belts, there is the potential for causing serious injury to a healthy person bearing even a moderate load over extended distances, due to fatigue in compensating for the load and balance. The problems are amplified for persons of limited physical capacity or with pre-existing health problems affecting their load carrying capacity.
There is another class of belt type devices, not related to backpacks, used in industries and occupations where heavy front lifting is encountered, and for related athletic activities such as weight lifting. These stand-alone corsets or back braces are generally characterized as being a girth strap or belt system configured for providing broad area backside or lumbar support, and are intended to prevent or reduce the likelihood of injury to back muscles when front lifting moderate to heavy loads as in picking up and moving boxes with one""s arms.
There is yet another class of belt type devices, not related to backpacks, used by the medical community in the treatment of abdominal conditions where additional support is deemed useful, such as in the containment or prevention of a possible abdominal rupture or hernia. The devices are variously known as abdominal support belts, corsets, or trusses. An abdominal support belt is minimally described as a girth strap of sufficient width or with a padded element for providing broad area support and inward pressure on the abdominal wall.
Patents and published materials on all of these arts are numerous. Patents that may provide the reader with additional context for understanding the disclosure that follows, include: Farris U.S. Pat. No. 5,676,293, issued Oct. 14, 1997, disclosing a backpack with a lumbar support and a rain hood, and claiming a xe2x80x9cwaist belt . . . to help support the backpack.xe2x80x9d; Hittenberge""s U.S. Pat. No. 1,619,513; issued Mar. 1, 1927, for an abdominal support belt system with an abdominal pad that is pressed into place with encircling spring members; and Cidissen""s U.S. Pat. No. 2,449,641, issued Sept. 21, 1948, for an abdominal support belt system for preventing abdominal rupture, featuring a wide belt and a lower-extending abdominal pad.
Publications that provide useful background for understanding the biomechanics of the human form factor as applied to lifting and load bearing. The article, Role of the Trunk in Stability of the Spine, by Morris, Lucas and Bressler, published in the Journal of Bone and Joint Surgery, April, 1961, describes the effect of a corset on intra-abdominal pressure and electro-myographic testing of abdominal and lumbar paraspinal muscles during lifting. Biomechanics of the Vertebral Column, by Troup, Physiotherapy, Vol. 65, No. 8, pp. 238-244, describes spinal mechanics and physiology in lifting. Mechanical Effectiveness Studies of Lumbar Spine Orthoses, by Nachemson, Schultz and Anderson, Department of Orthopedic Surgery, Sahlgren Hospital, University of Goteborg, Sweden, date of publication unknown, evaluates the physiology of lifting.
Intra-Abdominal Pressure During Trunk Extension Motions, by W. S. Marras and G. A. Mirka, Clinical Biomechanics, Vol. 11, No. 5, pp. 267-274, discusses the physiology of lifting. Biomechanics of the Spine, by M. Pearcy, Current Orthopedics, 1989, pp. 96-100, offers more discussion on the physiology of lifting. Finally, Effects of Back Support on Intra-Abdominal Pressure and Lumbar Kinetics during Heavy Lift, by M. L. Woodhouse, R. W. McCoy, D. G. Redondo, and L. M. Shall, published in Human Factors, 1995, Vol. 37(3), pp. 582-590, is a study of the biomechanical effects of weight lifting with and without lumbosacral supports.
Commercial products relating to this subject matter include the BackSaver(trademark) 3 in 1 sport belt, a corset type support belt into which magnets, or hot and cold pacs can be inserted, and the AirTec(trademark) backpack, a backpack with inflatable shoulder straps and an inflatable lumbar support pad but without a waist belt, both distributed by BackSaver Products Company of Holliston, Mass.
In summary, the prior art has long recognized that a hip belt attached to a shoulder strap backpack can relieve the load on a user""s spine by transferring a portion of the backpack load weight from the shoulders and spine to the pelvic region via the attachment to the hip belt. Other fields of art have recognized the benefits of back braces and abdominal support belts for purposes not relating to backpacks and back borne loads. But no one has explored the biomechanics of generating internal, non-skeletal, supplemental support for a back borne load by using intentional, significant abdominal support, in combination with external support off the pelvic region.
It should be noted at the outset that the inventors have about 50 years collective experience as regular recreational hikers and backpackers, and that all of the inventors are degreed and licensed medical practitioners, with the commensurate ability to read, understand and extrapolate the results of their own experiences, testing, and study of related biomedical published materials, leading to the development of the invention disclosed herein.
It is an object of the invention to provide a mechanism for utilizing abdominal-hydraulic pressure to aid in the support of shoulder, spine and pelvic supported, back borne loads.
It is another object to provide a simple device for use with existing backpacks with hip belts, employing abdominal pressure to generate internal support of the backpack load in combination with the external load support mechanisms.
It is yet another object of the invention to provide improved hip belts for use with backpacks, employing abdominal pressure to generate internal support of the backpack load in combination with the external backpack support mechanisms.
It is a still yet further object to provide a back borne load carrier system employing abdominal pressure to generate internal support of the load in combination with the external load support mechanisms.
These objectives are met with, simply stated, a backpack load carrier system with abdominal support, providing both internal and external modes of back borne load support to increase an individual""s back bearing load capacity and to reduce the likelihood of injury from carrying a loaded backpack.
In accordance with the invention, structure assuring significant abdominal support is provided for as additive to or part of a load bearing hip belt or backpack and hip belt combination, to cause a portion of the load weight that would otherwise be supported directly by the spinal column and externally off the hip belt, to be assisted by proper abdominal support and related hydraulic action through the abdominal trunk region for additional internal support of the spine and shoulders and hence of the load.
The structure providing the abdominal support may be a stand alone device for use with a hip belt and backpack, or be integrated into a load bearing hip belt or backpack and hip belt combination. In all cases, suitable structure is provided to assure that a large frontal area of abdominal pressure is applied to the user to aid the abdomen in its natural hydraulic muscle action in support of the loaded spinal column.
The principle employed in the invention is most simply explained as follows: The pelvic region, which includes the muscular walls of the back and abdomen, can be thought of as a hydraulic cylinder. The abdominal contents can be though of as the hydraulic fluid of the cylinder, providing interior support for the upper body in conjunction with the spine. The musculature of the abdominal wall completes the frontal portion of the cylinder. From another perspective, the phenomenon is somewhat analogous to the Sarmiento effect of using compressive forces on soft tissue to stabilize a long bone fracture.
The undertaking of an additional load or weight on the back, absent the invention, is automatically compensated for, initially, by a reflexive tensioning of the abdominal muscles to increase the pressure in the cylinder, allowing the bearer to retain most of his or her upright posture and carriage, while adjusting for the change in center of gravity by tilting or leaning somewhat forward.
However, this human cylinder wall is by nature flexible. Its ability to perform adequately with a load on its back is subject to fatigue, somewhat analogous to any flexible wall hose or the like that is working under pressure. In a relatively short period of time, depending on the condition of the bearer and the weight of the load, the cylinder wall begins to relax and the additional hydraulic support fades. Posture sags, stress and compression mounts on the shoulders and lower spine and pelvis, discomfort begins to be noticeable, and the potential for biomechanical stress injuries rises.
In accordance with the principles of the invention, the applicants""backpack load carrier incorporates a supplemental xe2x80x9ccylinderxe2x80x9d wall structure or girth strap and fall abdominal wall pad that is applied around the primary cylinder wall structure, the user""s abdomen, in such a manner as to improve the efficiency and prolong the useful cycle time of the cylinder for maintaining the pressure necessary to bear the extra load, before requiring a rest. The support structure contacting the abdominal region, however implemented, covers as much of the abdominal wall as is practical to achieve the greatest hydraulic effect.
The abdominal support structure can be provided in the form of a flexible, inelastic or minimally elastic abdominal pad or belt section that is held by opposing edges or ends in tension over a substantial area of the abdominal region by an inelastic hip belt that is adjusted in length so as to bring light but noticeable pressure to bear on the abdominal wall.
Alternatively, the abdominal support structure can be provided in the form of a separate abdominal pad, utilized as a compression member under a belt, a generally oval pad fabricated with conforming surface shape and of sufficiently rigid construction by choice of material and molding techniques to be installed within the girth of a separate hip belt so as to contact and bear uniformly against a large area of the abdominal wall, and to prevent the belt and/or buckle from deforming or penetrating the pad when the belt is put in tension about the user""s pelvic region. In other words, it must be sufficiently rigid to be able to uniformly distribute the belt and buckle pressure of typical hip belts uniformly across a large area of the abdominal wall.
The minimum size of the abdominal support structure, for providing meaningful internal support in the context of load carrying, characterized as a scaleable factor to fit any user, has been determined to be a length, spanwise about the user, of at least one half the distance between the bony landmarks created by the Anterior/Superior Iliac Spines (ASIS) of the user""s pelvis. The minimum width, or height as applied to the user, is one half of the distance between the lower costal margin and the mid inguinal ligament. The device is sized and placed to avoid limiting bending at the waist and flexing at the hips. The support structure does not disturb abdominal breathing.
The girth or hip strap is connected at the back or sides to the backpack or load and is sufficiently wide and well secured above the user""s hips so as to concurrently provide a degree of direct, external load support, in addition to providing its hydraulic, internally supporting effect. The abdominal support function requires that the belt be flexible to conform readily to the user""s pelvic shape, but not elastic or stretchable, so that circumfrential length and average abdominal pressure can be maintained during normal body motion and flexure. The dual functionality of the invention in providing both internal and external support will be readily apparent in the description of the preferred embodiments and claims that follow.
Other objects and advantages of the present invention will likewise become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described several preferred embodiments of the invention, simply by way of illustration of the best modes contemplated by us for carrying out our invention.